BP Spill May Be Less Than Doomsayers Think: Tadeusz W. Patzek

June 23 (Bloomberg) -- Two months have passed since the
blowout of the BP Plc exploratory Macondo well in the Gulf of
Mexico. Much more is now known about a string of fateful
decisions taken in the course of drilling this well.

Individually, none of BP’s decisions would have caused the
blowout, but their confluence led almost inevitably to the
largest oil-related tragedy in U.S. history. Eleven people have
died, a whole coastal region of the Gulf of Mexico has been
devastated and it is uncertain that BP will survive the ordeal.

There is some good news, however: Most of the oil and gas
spewing from the failed well is now being captured by BP
engineers. Here is why.

On June 17, video feeds showed oil and gas to be still
escaping from the containment hat attached to the failed blowout
preventer (BOP) on top of the well. The brown part of the plume
consists of oil droplets, while the white bubbles are gas
encapsulated in hydrate ice skins. These ice-gas bubbles
eventually dissolve in seawater, thus they never reach the ocean
surface.

I have watched the BP video feeds for weeks. The plume
currently overflowing the top hat is significantly smaller and
less violent than the initial oil and gas plume emanating from
the broken riser. This suggests that a large portion of the well
flow is now being produced in a controlled fashion.

On June 16, BP finally managed to connect the choke and
kill lines below the BOP to a surface collection system onboard
the Q4000 vessel. Both production lines (the top-hat riser and
the choke-and-kill line riser) are capable of collecting around
25,000 barrels of oil and 30 million standard cubic feet of gas
daily. Correcting volumes for the pressure difference between
the sea bottom and the surface, the total flow of oil and gas
through the BOP should be about 35,000 barrels a day, not 60,000
barrels a day as some claim.

Increased Flow

There are two reasons why the oil flow rate from the failed
BP well may have increased from the initial 9,000 to 22,000
barrels a day, the amount estimated to have been leaking in May.
First, the partially closed rams and rubber rings functioning as
flow barriers in the BOP may have been eroded by oil and gas,
and perhaps sand. Second, “wormholes,” or meandering flow
tubes that connect the reservoir and the well, may have formed.

“Wormholes” are created when sandstone crumbles and
washes away because either the oil and gas flow rate is high, or
the reservoir oil is highly viscous, like cold molasses. The
combined effect of rock and well erosion might have increased
oil flow from about 20,000 to 30,000 barrels a day.

Soil in the Rain

The physics of this phenomenon, akin to washing soil away
by rain, is nicely described on The Oil Drum website. Gas is an
additional 50 percent of the total flow and is often conflated
with the oil flow. As I indicated at the beginning, gas
dissolves in the seawater at depth and doesn’t reach the ocean
surface.

For the sake of perspective, consider the BP Thunder Horse
platform, the world’s largest semisubmersible facility. Prior to
the disastrous spill it was also the most productive platform in
the Gulf of Mexico, located in water that’s about 6,050 feet
(1,844 meters) deep. As of March 20, 2009, daily production at
this platform was approximately 260,000 barrels of oil and 210.5
million standard cubic feet of natural gas a day from seven
wells, an average of 37,000 barrels of oil and 30 million
standard cubic feet of gas per well.

The former Minerals Management Service reports that the
majority of ultra-deepwater wells in the Gulf of Mexico produce
around 20,000 barrels of oil a day, with the best well in the
entire region producing 41,000 barrels a day.

Failure Not Likely

Unless there has been a complete failure of the central 7-inch production casing -- which I don’t believe has occurred --
then no reason exists to believe the failed Macondo well is
producing 60,000 barrels of oil a day.

Based on the available information and calculations, it is
highly probable that the failed BP well is producing oil at a
rate that is closer to 20,000 or 30,000 barrels of oil a day. If
BP is currently collecting 25,000 barrels a day, then only some
5,000 barrels of oil are being spilled in the Gulf waters.

Based on the evidence presented thus far, it seems quite
unlikely that 60,000 to 150,000 barrels of oil a day will ever
flow from the Macondo well. By controlling the spill rate, BP
has gained the breathing room required to successfully complete
the bottom kill using the relief wells. I anxiously await the
good news that the Macondo well has ceased flowing.

(Tadeusz W. Patzek is chairman of the petroleum and
geosystems engineering department at the University of Texas-Austin. The opinions expressed are his own.)